The prefecture has some archaeological sites going back to the Jōmon period (around 400 BCE). About 3,000 years ago, Mount Hakone produced a volcanic explosion which resulted in Lake Ashi on the western area of the prefecture.

CommodoreMatthew Perry landed in Kanagawa in 1853 and 1854 and signed the Convention of Kanagawa to force open Japanese ports to the United States. Yokohama, the largest deep-water port in Tokyo Bay, was opened to foreign traders in 1859 after several more years of foreign pressure, and eventually developed into the largest trading port in Japan. Nearby Yokosuka, closer to the mouth of Tokyo Bay, developed as a naval port and now serves as headquarters for the U.S. 7th Fleet and the fleet operations of the Japan Maritime Self-Defense Force. After the Meiji period, many foreigners lived in Yokohama City, and visited Hakone. The Meiji Government developed the first railways in Japan, from Shinbashi (in Tokyo) to Yokohama in 1872.

The epicenter of the Great Kantō earthquake in 1923 was deep beneath Izu Ōshima Island in Sagami Bay. It devastated Tokyo, the port city of Yokohama, surrounding prefectures of Chiba, Kanagawa, and Shizuoka, and caused widespread damage throughout the Kantō region.[4] The sea receded as much as 400 metres from the shore at Manazuru Point, and then rushed back towards the shore in a great wall of water which swamped Mitsuishi-shima.[5] At Kamakura, the total death toll from earthquake, tsunami, and fire exceeded 2,000 victims.[6] At Odawara, ninety percent of the buildings collapsed immediately, and subsequent fires burned the rubble along with anything else left standing.[7]

In 1945, Kanagawa was the 15th most populous prefecture in Japan, with the population of about 1.9 million. In the years after the war, the prefecture underwent rapid urbanization as a part of the Greater Tokyo Area. The population as of September 1, 2014, is estimated to be 9.1 million.[8] Kanagawa became the second most populous prefecture in 2006.

Kanagawa is a relatively small prefecture located at the southeastern corner of the Kantō Plain[9] wedged between Tokyo on the north, the foothills of Mount Fuji on the northwest, and the Sagami Bay[9] and Tokyo Bay on the south and east. The eastern side of the prefecture is relatively flat and heavily urbanized, including the large port cities of Yokohama and Kawasaki.

The southeastern area nearby the Miura Peninsula is less urbanized, with the ancient city of Kamakura drawing tourists to temples and shrines. The western part, bordered by Yamanashi Prefecture and Shizuoka Prefecture on the west,[10] is more mountainous and includes resort areas like Odawara and Hakone. The area, stretching 80 kilometres (50 mi) from west to east and 60 kilometres (37 mi) from north to south, contains 2,400 square kilometres (930 sq mi) of land, accounting for 0.64% of the total land area of Japan.[10]

The Tama River forms much of the boundary between Kanagawa and Tokyo. The Sagami River flows through the middle of the prefecture. In the western region, the Sakawa (river) runs through a small lowland, the Sakawa Lowland, between Hakone Volcano to the west and the Ōiso Hills to the east and flows into Sagami Bay.[9]